Touchscreens are widely used in devices, such as personal computers, tablet computers, entertainment systems, game consoles, and cellular telephones for data input and/or controlling cursor movement. One common type of touchscreen uses a capacitive sensing system, to sense and measure proximity, position, displacement or acceleration of an object, such as a finger or stylus. The capacitive sensing system generally may include a matrix or array formed by etching parallel layers of conductive material separated by a layer of insulating material to form lines of receive and transmit electrodes with a sensing capacitor at each intersection of the receive and transmit electrodes. A voltage pulse (Tx) is applied to a transmit electrodes and the accumulated charge on each receive electrode or channel sensed and measured to detect a change in capacitance due to proximity of a conductor, such as a finger, to the touchscreen.
One way to sense a capacitance is to convert it to charge and measure the charge quantity. Charge and capacitance are related by Q=CV where Q=charge, C=capacitance and V=voltage. These capacitance sense solutions convert the capacitance into charge by modulating the voltage across it and integrating the resulting current. One conventional capacitance sensing system uses two parallel integration capacitors in feedback with a switched capacitor (SC) integrator. One capacitor is always integrating while the second can be reset in parallel. Thus, each receive (RX) channel may include two relatively large capacitors. This results in increased circuit complexity, cost and, more important, increased circuit size.